Hydraulic coupling device, as well as brake system with such a coupling

ABSTRACT

Hydraulic brake systems are known wherein, for the purpose of brake control, a counterforce is built up in the booster (60) for actuation of the master brake cylinder which results in unloading the master brake cylinder. What is disadvantageous in the known system is that this counterforce also resets the pedal (pedal piston 3) so that vehement pedal movements will result from the control action. Therefore, our present invention suggests to interpose a transmission device (3, 4, 5, 6, 7) between the pedal and the actuator (booster) enabling to decouple actuator and pedal.

A brake system is described in German published patent application 33 17629, the master brake cylinder of which is force-applied by apedal-actuated booster. This booster comprises a valve which, independence upon the pedal force, develops an amount of pressure in thebooster which loads the master brake cylinder in addition to the pedalforce. Under the effect of the introduced pressure, a wall in thebooster moves towards the master brake cylinder and thereby causes adecrease of the working chambers of the master brake cylinder. Further,the above published patent application describes the possibility ofrealising brake slip control, that means of avoiding locking of thewheels by reducing the pressure in the wheel brakes. This is effected inthat a counterpressure is built up in the booster which results inunloading the master brake cylinder because it acts upon the wall inopposition to the pedal force. Valves are inserted into the brake lineswhich are open only when the pressure is to be reduced in the associatedwheel brake cylinders. When the pressure has been reduced, the wheel canre-accelerate so that renewed braking pressure build-up becomesnecessary after a while. To this end, the counterforce is `withdrawn`from the booster, i.e. reduced, so that renewed build-up of pressuretakes place in the master cylinder which is supplied further to thewheel brakes. Previously, the wheels had been able to sufficientlyre-accelerate, and now they have to slow down again. The wall of thebooster is constantly moving to and fro during a like control action andentrains the control valve. Since the pedal is coupled directly with thevalve in previously known designs, the pedal performs a movement to andfro during the brake slip control action. This may even be desirable toa certain degree, since thus there is the possibility of informing thedriver that a brake slip control action is performed. However, it hasshown that these movements are too vigorous under certain circumstancesand are felt as disturbing by the driver. From this derives the objectto devise the coupling between the actuator, which actuates the masterbrake cylinder, and the pedal in such a fashion that the movements ofthe booster wall (of the actuator) are not transmitted onto the brakepedal. Moreover, the possibility must be afforded that the driver caninfluence the pressure in the wheel brakes by reducing the pedal force.This object is achieved by virtue of a hydraulic coupling as isdescribed in claim 1.

The design becomes particularly simple when the pistons are guided inone common housing bore.

In a favourable manner, the pedal piston has a portion of smallercross-section which extends through a wall in a sealed relationshipthereto and which can be accommodated in an axial bore of thecompensating piston for the purpose of guiding.

The wall isolates two chambers from each other which are interconnectedfor the hydraulic coupling. The chambers are filled with incompressibleliquid so that, caused by the movement of the pedal piston, pressurefluid is displaced out of the blocking chamber into the compensatingchamber and urges the actuator piston to advance.

For decoupling the pedal piston and the actuator piston, the blockingchamber is shut off hydraulically so that the pedal piston is no moreactuatable in the actuating direction, and the compensating chamber isconnected to a receiving chamber so that the actuator piston is freelymovable.

The said receiving chamber can be a simple open supply reservoir, or aclosed accumulator having a piston which is movable in opposition to aspring. The spring force generates a pressure in the accumulator whichacts upon the actuator instead of the pedal force.

To this end, the accumulator piston is biassed by a spring against stopsso that the spring force does not convert into a hydraulic pressure atfirst. When now pressure fluid is pressed out of the compensatingchamber into the accumulator, the piston lifts from its stops, and thespring generates a pressure in the accumulator chamber which becomeseffective in the compensating chamber as well. The preloading force ofthe spring is chosen such that the pressure in the compensating chamberexerts such a force on the actuator piston that the control valveassumes its maximum opening position. Further explanations will followin the description of the Figures.

Another advantageous embodiment arranges for the pedal piston to have asurface which is adjacent to the compensating chamber.

As has been explained already, the hydraulic coupling device can beinserted in a particularly favourable manner in anti-lock brake systemswherein the booster (actuator) is exposed to a counterpressure for brakeslip control, and wherein the force-transmitting wall of the booster isslid back in opposition to the pedal force. As soon as slip control isnot necessary, the pedal piston is coupled hydraulically to the actuatorpiston so that the movement of the pedal is transmitted directly ontothe actuator. As soon as brake slip control commences, the pedal pistonand/or the blocking chamber is blocked hydraulically so that the pedalis not displaceable in the actuating direction. As the compensatingchamber is communicating with the receiving chamber, the actuatingpiston is freely movable so that the movement of the booster wall is nottransmitted onto the pedal piston.

To satisfy safety aspects, it can be expedient to movably support thehousing of the force-transmitting device and to have it border on ablocking chamber. The latter is blocked hydraulically so that thehousing is fixed in position. Should the control valve of thetransmitting device get jammed and the pedal chamber remainshydraulically blocked thereby, the blocking chamber can be opened sothat, for brake application, the housing is displaced under the effectof the pedal force, the pedal force being supported on the actuatorpiston via the housing. The inventive idea shall now be explained inmore detail by way of several embodiments.

FIG. 1 through FIG. 3 show various embodiments of the transmittingdevice,

while FIGS. 4 and 5 show brake systems including a force-transmittingand/or decoupling device.

Identical and/or identically acting component parts have been assignedlike reference numerals in FIGS. 1 to 5. First, FIG. 1 shall be referredto.

The transmitting device is substantially composed of a housing 1containing a longitudinal bore 2 in which two pistons are sealinglyguided. The housing 1 itself is attached to the housing of a brake powerbooster 60 by way of a catch mechanism 23. The said pistons are theactuator piston 4, on the one hand, which is coupled to the push rod foroperating the brake valve 61, and the pedal piston 3, on the other hand,which is coupled to a non-illustrated pedal. Said pedal piston 3comprises a tapering portion which extends sealingly through a wall 9and which is guided in an axial bore of the actuator piston 6. This wall9 is represented by a seal in this embodiment. An annular chamber, theso-called blocking chamber 5, is arranged between the seal 9 and themain part of the piston 3 as well as the tapering portion of the piston3 and the wall of the bore 2. The compensating chamber 6 is locatedbetween the wall 9 and the actuator piston 4. Blocking chamber 2 andcompensating chamber 6 are interconnected via a connecting line 10 inwhich the control valve 7 is inserted. In the initial position of thisvalve, the chambers 5 and 6 are interconnected. In the switchingposition of the valve, the blocking chamber 5 is hydraulically blocked,and the compensating chamber 6 communicates with the accumulator chamber24. In this embodiment, the accumulator 81 is substantially composed ofa piston 21 which is loaded by a spring 20 and which confines theaccumulator chamber 24. When pressure fluid is supplied into theaccumulator chamber 24, the piston 21 displaces in opposition to theforce of the spring 20. When the accumulator chamber 24 has its smallestvolume, piston 21 abuts on two contact pins 22 and establishes aconductive connection between these contact pins. This way, it can befound out whether the accumulator is filled or empty.

In this embodiment, the actuator is represented by a brake power booster60 which comprises a movable wall 62 which subdivides the housing of thebrake power booster 60 into a modulator chamber 63 and a control chamber64. Arranged on the wall 62 are a valve of known construction as well asa push rod 65 which acts upon the non-illustrated master cylinder and/ormaster cylinder piston. By means of two valves 66, the modulator chamberis connected to a vacuum source vac, in general this is the suction areaof a combustion engine, and to the atmosphere atm, respectively. Bymeans of another valve 67, via the intermediary of the control valve 61,the chamber 64 can now also be connected either to the vacuum source vac67 or to the atmosphere atm. In the non-actuated position of the valve61, the chambers 63 and 64 are interconnected. The vacuum of the vacuumsource is prevailing in them. When the valve is actuated, first thechambers are separated from each other, then chamber 64 is connected tothe atmosphere via the valve 67 in a dosed manner and proportional topedal force.

The system operates according to the following scheme:

In the basic position, all parts assume the position shown, the valvesare in their illustrated switching positions. To initiate a brakingoperation, the driver operates a pedal not shown, as a result whereofthe piston 3 is displaced to the left according to the illustration. Thepressure fluid in the chambers 5 and 6 acts as a hydraulic cushion sothat the actuator piston 4, too, is displaced. The valve 61 is actuatedin the fashion described hereinabove so that air flows into the chamber64, and the wall 62 is shifted to the left under the effect of the airpressure. The tappet 65 acts upon a master brake cylinder, consequently,a pressure develops therein which is supplied further into the wheelbrakes.

The rotational behaviour of the wheels is constantly monitored by meansof sensors, whose signals are delivered to the electronic unit 68. Upondetection of an imminent locked condition of one of the wheels, firstvalve 7 is switched over. This has as a consequence that chamber 5 isshut off hydraulically and that piston 3 is not displaced further, noteven when the pedal force is augmented. The compensating chamber 6 isnow communicating with the reservoir 81 so that pressure fluid can beexchanged between the chamber 6 and the accumulator chamber 24. Whenpressure fluid is displaced out of chamber 6 into the accumulatorchamber 21, pressure will develop in the chamber 6 and the accumulatorchamber 22, respectively. This pressure, in lieu of the pedal force, isnow acting upon the brake valve so that the latter assumes a position inwhich the connection between the chambers 63 and 64 is interrupted andthe connection between the chamber 64 and the valve 67 is open(actuating position). The valves 66 are now switched over so thatatmospheric pressure is applied to chamber 63 and the pressure of thevacuum source is applied to chamber 64. This has as a result that thewall 62 is shifted to the right according to the drawing, whereby themaster brake cylinder is relieved from load. The actuation of thebooster is now performed according to a predefined control algorithmirrespective of the pedal force.

As soon as the driver is no longer applying load on the pedal, piston 3moves to the right. Pressure fluid out of the accumulator chamber 24flows via the chamber 6 and the seal 9 acting as a non-return valve intothe chamber 5. As soon as the piston 21 has reached the contact pins 22,valve 7 changes over so that now it assumes its basic position again.The brake force is again defined by the pedal force so that this way therespective maximum brake force can be determined by the driver. Thus,the possibility continues to exist of intervening in a control action,that means to interrupt it, by unloading the brake pedal.

Hence, the idea resides in actuating the booster in the control phase insuch a way that the control valve 61 closes the connection between thechambers 63 and 64 and opens the connection between chamber 64 and valve67. The chambers 63 and 64 can now be connected independently of eachother to a vacuum source (vac) or to the atmosphere (atm) by means ofthe valves 66 and 67.

FIG. 2 depicts a slightly varied version of the force-transmittingdevice of FIG. 1. The piston 3 is composed of two piston parts 30a, 30bwhich are interconnected via a stem 31 which extends sealingly through awall 9. The one part 30a is acted upon the pedal force, whilst part 30blies opposite to the piston 4. The hydraulic connection of the chambers5 and 6 is such that, in the basic position of valve 7, chamber 6 isshut off hydraulically and serves as a transmission chamber for theforces between the pedal and the actuator, and chamber 5 connects to thesupply reservoir 8. Said chamber 5 is shut off hydraulically bychange-over of valve 7 so that piston 3 can no more be moved in theactuating sense. Chamber 6 is connected to the unpressurized supplyreservoir 80 so that there is free movability of the actuator piston 4.As an additional element, a pressure switch 11 is provided herein whichmonitors the pressure in the blocking chamber 5 and furnishes areference value for the pedal force. When the driver takes his foot fromthe pedal, the pressure in the blocking chamber 5 will decrease, thusallowing a braking pressure control operation to be interrupted.

Another pressure switch 40 monitors the pressure in chamber 6. Saidchamber 6 is moreover connected to the supply reservoir via a non-returnvalve 41 and 41', respectively. This non-return valve can be housed inthe partial piston 30b, for instance.

The embodiment according to FIG. 2 operates essentially according to thesame scheme like the embodiment of FIG. 1.

The control valve 7 assumes the illustrated position for forcetransmission. Chamber 6 is shut off hydraulically, chamber 5 is incommunication with the supply reservoir. Pressure fluid is displaced outof chamber 5 into the pressure-fluid reservoir 80 upon movement of thepiston 3. The pressure fluid in chamber 6 acts as a hydraulic pressurecushion and transmits the movement of piston 3 onto piston 4.

The valve 7 is changed over in a brake slip control operation. Chamber 5is shut off hydraulically so that piston 3 is fixed. Piston 4 is nowfreely movable, since pressure fluid is displaced out of chamber 6 intothe supply reservoir upon a corresponding movement of the piston 4.

In order to allow a supply reservoir 80 instead of an accumulator 81 toconnect to the compensating chamber 6, the ports of valve 61 must bedesigned somewhat differently. The port which terminates into chamber 63according to FIG. 1 must extend to an outside port on the housing ofbooster 60, e.g. via a hose line. This port can then connect to eitherthe vacuum source or the atmosphere by virtue of a valve, the functionof which corresponds to valve 67. The actuator piston 4 is not loaded ina control action so that chamber 64 can be connected either to thevacuum source or to the atmosphere via the port described above. Asdisclosed in FIG. 2, chamber 63 is likewise connectible via the valves66 either to the vacuum source or to the atmosphere.

The braking pressure can be continuously influenced by the driver due tothe fact that chamber 5 communicates via a non-return valve either tothe master brake cylinder or to the wheel brakes. The pressure in themaster brake cylinder and/or in the wheel brakes will then not bepermitted to be in excess of the pressure which is built up in chamber 5by the driver.

Another embodiment is depicted in FIG. 3. The control valve 7 is hereindesigned as a slide valve which is accommodated in the wall betweenchamber 5 and chamber 6. In the illustrated initial position, there is apressure-fluid connection between the two mentioned chambers via thechannel 10 in the wall 9. Chamber 5 is shut off hydraulically when therotary slide valve is turned by 90 degrees. Chamber 6 is connected tothe supply reservoir 80.

Another special characteristic in this embodiment resides in theprovision of a blocking chamber 51 which is designed in an intermediatemember 50. Chamber 51 is confined by the housing 1 of the transmittingdevice and connects to the supply reservoir 80 via a closing valve 52.This valve is normally open. When hydraulic force transmission takesplace between the pistons 3 and 4, then housing 1 is not moved, sincethe forces which are transmitted via the spring 54 from the pedal ontothe housing are compensated by the spring 53. As explained, chamber 5 isshut off hydraulically during a brake slip control operation so that thepressure forces would be transmitted onto the housing. A movement of thehousing resulting therefrom is prevented by the valve 52 switching overso that chamber 51 is shut off hydraulically.

Should the case occur that valve 7 is jammed so that chamber 5 remainshydraulically closed, an actuation of the brake would be no morepossible according to the preceding embodiments, since the pedal forcescannot be transmitted onto the actuator piston. This problem is solvedin the embodiment according to FIG. 3. This is because if this caseoccurs without a slip control action being planned at the same time,valve 52 will open, whereby the housing is displaced under the influenceof the pedal force and moves into abutment on the actuator rod 4. Thisway, a transmission of the pedal forces onto the actuator and thus ontothe master brake cylinder is possible.

The stops 55 bring about a defined initial position of the housing 1.

This embodiment, too, provides for a pressure sensor 11 which monitorsthe pressure in the chamber so that the brake slip control operation canbe interrupted as soon as the driver retracts his foot from the pedal.

An improvement not shown resides in that another closing valve which isopen in its initial position is inserted into the channel 10 between therotary slide and the blocking chamber 5. Upon commencement of a brakeslip control operation, first this additional valve is closed before thecontrol valve 7 is actuated. At the end of the brake slip controloperation, the valves are reset in the reverse order.

FIGS. 4 and 5 illustrate the mounting of a force-transmitting deviceinto a brake system. This brake system is composed of a master brakecylinder 71 as well as an actuator 70, which is an electromagneticcontrol member in this instance. Disposed between the symbolicallyillustrated pedal and the actuator is the decoupling device 12 asdescribed e.g. in FIGS. 1 to 3. The pedal forces are recorded by meansof a force sensor 72, the pedal travel is recorded by means of a travelsensor 73. Connected to the master brake cylinder 71 via two brakecircuits I and II are the wheel brakes which are referred to by theirplace on the vehicle (v=front, h=rear, l=left, r=right). Each wheelbrake is furnished with a valve 74. A braking operation is initiated byapplication of the pedal, whereby the pedal forces are transmitteddirectly onto the master brake cylinder. The pedal forces are boosted,for instance by a pneumatic booster 60 (FIG. 5) or by theelectromagnetic means 70 which supplies a force component correspondingto the pedal force and/or the displacement travel of the pedal. At theonset of the brake slip control operation, the transmitting device 12 isactivated, the pedal being decoupled from the actuator 70 as a result.This actuator is now transmitting forces onto the master cylinder 71corresponding to the algorithms of brake slip control and inconsideration of the pedal forces.

We claim:
 1. A hydraulic coupling for transmitting longitudinal forcefrom a brake pedal to an actuator for actuating a master brake cylinderof a brake system, said hydraulic coupling comprising:a housing; a pedalpiston connectable to said brake pedal and disposed in the housingdefining a blocking chamber within the housing; an actuator pistonconnectable to said actuator and disposed in the housing defining acompensating chamber within the housing; a hydraulic fluid receivingchamber external of the housing; and a valve operable to hydraulicallyisolate the blocking chamber while connecting the compensating chamberto the receiving chamber.
 2. The hydraulic coupling of claim 1 furthercomprising said housing having one common bore for guiding the pedalpiston and the actuator piston.
 3. The hydraulic coupling of claim 1further comprising said actuator piston having an axial bore and saidpedal piston having a narrowed portion engageable within the axial boreof the actuator piston.
 4. The hydraulic coupling of claim 3 furthercomprising said housing having a wall with a bore extending therethroughsuch that said narrowed portion of said pedal piston extends through thebore in a sealed relationship to the wall.
 5. The hydraulic coupling ofclaim 1 wherein said blocking chamber is interconnected with saidcompensating chamber for force transmission.
 6. The hydraulic couplingof claim 1 wherein said blocking chamber is isolated hydraulically andsaid compensating chamber is connected to said receiving chamber fordecoupling said pedal piston from said actuator piston.
 7. The hydrauliccoupling of claim 1 further comprising a three-way/two-positiondirectional control valve movable between a first position wherein saidblocking chamber is interconnected with said compensating chamber forforce transmission and a second position wherein said blocking chamberis isolated hydraulically while said compensating chamber is connectedto said receiving chamber for decoupling said pedal piston from saidactuator piston.
 8. The hydraulic coupling of claim 1 further comprisingcatch means for snap fitting said housing on said actuator.
 9. Thehydraulic coupling of claim 1 wherein said receiving chamber comprisesan accumulator.
 10. The hydraulic coupling of claim 9 further comprisingsensor means for sensing a fluid level within said accumulator.
 11. Thehydraulic coupling of claim 9 further comprising a movable wall disposedwithin said accumulator, a spring biasing said movable wall within saidaccumulator, and two switching contacts spaced from one another facingthe movable wall such that the movable wall forms a bridge between saidcontacts in a normal spring biased rest position.
 12. The hydrauliccoupling of claim 1 further comprising a wall isolating said blockingchamber from said compensating chamber, the wall having a pressure fluidchannel for interconnecting the chambers, and a three-way/two-positiondirectional control valve disposed within the channel for interruptingthe connection between said blocking chamber and said compensatingchamber.
 13. The hydraulic coupling of claim 12 wherein saidthree-way/two-position directional control valve comprises a rotaryslide valve.
 14. The hydraulic coupling of claim 1 further comprisingsaid pedal piston having a first part adjacent said compensatingchamber.
 15. The hydraulic coupling of claim 14 further comprising saidpedal piston having a second part interconnected with said first part byan intermediate stem, said housing having a wall disposed between saidfirst and second parts of said pedal piston, the wall having a boreallowing passage of the intermediate stem in a fluid tight manner, thesecond part of said pedal piston disposed between said pedal and thefirst part, the second part of the pedal piston defining said blockingchamber in an annular chamber between the wall and the second part ofsaid pedal piston, and the first part of said pedal piston forming anend boundary of said compensating chamber.
 16. The hydraulic coupling ofclaim 15 wherein said compensating chamber is connected to saidreceiving chamber while said blocking chamber is hydraulically isolated.17. The hydraulic coupling of claim 15 wherein said blocking chamber isconnected to said receiving chamber while said compensating chamber ishydraulically isolated.
 18. The hydraulic coupling of claim 14 furthercomprising first pressure sensor means for monitoring said blockingchamber and second pressure sensor means for monitoring saidcompensating chamber.
 19. The hydraulic coupling of claim 1 furthercomprising said actuator having a connecting portion and said housingsealingly guided in the connecting portion of said actuator with saidblocking chamber disposed adjacent said housing being hydraulicallyisolatable.
 20. The hydraulic coupling of claim 19 further comprising astop in abutment with said housing, and spring means for normallyretaining said housing in abutment with the stop, wherein said blockingchamber has maximum volume when said housing is in abutment with thestop.
 21. A hydraulic brake system comprising:means for generating slipcontrol signals; a master brake cylinder; an actuator acting on themaster brake cylinder such that the master brake cylinder can be loadedand unloaded in dependence on the slip control signals by actuating theactuator; a brake pedal; a hydraulic coupling disposed between theactuator and the brake pedal for transmitting longitudinal force fromthe brake pedal to the actuator for actuating the master brake cylinder,the hydraulic coupling including: a housing; a pedal piston connectableto said brake pedal and disposed in the housing defining a blockingchamber within the housing; an actuator piston connectable to saidactuator and disposed in the housing defining a compensating chamberwithin the housing; a hydraulic fluid receiving chamber external to thehousing; and a valve operable to hydraulically isolate the blockingchamber while connecting the compensating chamber to the receivingchamber.
 22. The hydraulic brake system of claim 21 wherein saidactuator comprises a pneumatic vacuum booster.
 23. The hydraulic brakesystem of claim 21 wherein said actuator comprises anelectromagnetically actuated control member.
 24. An anti-lock brakesystem comprising:a plurality of wheel brakes; a closable valveassociated with each wheel brake; a master brake cylinder having atleast one working piston, the master brake cylinder connected to thewheel brakes through each associated closable valve; a booster insertedin front of the master brake cylinder and including a movable wallsupported on at least one working piston of the master brake cylinder,the movable wall separating two chambers, the two chambers selectivelyand independently connectable to a pressure source and to a vacuumsource for loading and unloading the master cylinder; a control valvefor introducing pressure fluid from the pressure source into one of thetwo chambers, said one of the two chambers being disposed on a side ofthe movable wall remote from the master cylinder, the control valveinterconnecting the two chambers in an initial position; a housinghaving a compensating chamber and a blocking chamber; an actuator pistondisposed in the housing for actuating the control valve, the actuatorpiston defining a boundary surface of the compensating chamber; apedal-operated pedal piston disposed within the housing defining aboundary surface of the blocking chamber; and an accumulator having anaccumulator chamber confined by a spring-loaded piston; wherein thecompensating chamber selectively communicates with the blocking chamberand, for a brake slip control operation, the compensating chamberselectively communicates with the accumulator chamber.
 25. The anti-lockbrake system of claim 24 further comprising a stop within theaccumulator and a spring biasing the spring-loaded piston against thestop.
 26. The anti-lock brake system of claim 25 wherein the spring isselected for a bias in excess of a maximum boosting power for thebooster.
 27. The anti-lock brake system of claim 24 wherein the pressuresource comprises atmosphere and wherein the pressure drain comprises avacuum source.
 28. The anti-lock brake system of claim 24 wherein thecontrol valve is disposed in the movable wall of the booster.